1. Field of the Invention
The present invention relates to a total reflection X-ray fluorescence analysis method. Specifically, the present invention is used for a high-sensitivity total reflection X-ray fluorescence analysis.
2. Background Art
In total reflection X-ray fluorescence analysis, excited X-rays are made incident on the surface of a subject, under a total reflection condition, and X-ray fluorescence emitted from an impurity in the surface of the subject is detected by a semiconductor detector provided above the subject, thereby analyzing a very small amount of impurity element on the surface of a semiconductor substrate with a high sensitivity, and minimizing the scattering of excited X-rays and the influences of X-ray fluorescence emitted from the subject bulk.
In order to analyze impurities on a surface of a semiconductor substrate with a high sensitivity, a chemical analysis methods such as WSA (Wafer Surface Analysis) or VPD (Vapor Phase Decomposition) is also widely used. In WSA, a surface of a semiconductor substrate is exposed to an acid vapor to dissolve an oxide layer, and the surface of the substrate is scanned with a small amount of an acid solution to take impurities on the surface and the oxide layer in the solution. The impurity concentration in the solution is measured using Atomic Absorption Spectrometry (AAS), Inductively Coupled Plasma Mass Spectroscopy (ICP-MS), etc. to analyze impurities on the substrate surface.
Recently, an ultra high-sensitivity impurity analysis method as disclosed in Japanese Patent Nos. 2,604,037 and 3,249,316 has become available, in which total reflection X-ray fluorescence analysis and WSA are combined. In such a method, a solution containing an impurity is dried on a mirror substrate, and the dried residue is measured using total reflection X-ray fluorescence analysis. Using this ultra high-sensitivity impurity analysis method, it is possible to perform an ultra high-sensitivity analysis, which is comparable to WSA employing ICP-MS, without any special skill or experience.
However, when the technique disclosed in Japanese Patent No. 2,604,037 is used, it is necessary to concentrate and dry an impurity collecting solution so as to be in a range detectable by a semiconductor detector under conditions satisfying the total reflection condition. In addition, the sensitivity tends to be lowered due to the influences of the absorption and the scattering of X-ray fluorescence caused by the silicon matrix contained in the collecting solution. Accordingly, at present, the subjects that can be measured using this technique are very limited. When the technique disclosed in Japanese Patent No. 3,249,316 is used, there are problems in that when only the acid vapor exposure is performed as a pretreatment before performing a total reflection X-ray fluorescence analysis, the pretreatment is highly dependent on the surface condition of the substrate, thereby varying the measurement result, and that since the analysis area is small, the sensitivity is degraded by one to two orders as compared to a case where the scanning and the collecting are performed using the acid solution after the exposure.